Switch device



R.P.MORK

SWITCH DEVICE June 26, 1951 Filed May 29, 1948 Kaymand I 1? MarkINVENTOR. By 615mm W Patented June 26, 1951 UNITED STATES PATENT OFFICESWITCH DEVICE poration of Ohio Application May 29, 1948, Serial No.30,086

19 Claims. 1

My invention relates to electric switches such as may be caused to closeone or more circuits when actuated by a key or other operating means.

A more restricted aspect of my invention has to do with the provision ofcontact switches, whereby an electric circuit may be closed graduallythrough a continuously variable resistance. Such switches may be used,for example, in conjunction with playing keys in electric musicalinstruments for connecting sources or" electric oscillationscorresponding to musical tones to output and sound producing devices forefiecting a gradual onset and release of the tones, thus eliminatingfrom the tones undesirable transients. commonly known as'key clicks orthumps, and producing a slower and more pleasing rise and fall of thetones.

Previously known practical switches of this type have been comparativelycostly to manufacture, requiring extremely close control ofmanufacturing, inspection and assembly operations.

The primary object of my invention is to provide a simple, reliableswitch unit or component which can be produced in large quantitiesquickly and cheaply, and which will be positive and reliable in itsaction.

It is an object to provide an assembly of such switch units by means ofwhich assembly a plurality of circuits may be closed substantiallysimultaneously by a single actuator.

It is an object of my invention to provide a simple, economical anddependable switch unit or assembly of the gradual contact or resistivetype.

Another object of my invention is to provide new and useful combinationsof electric contact materials in switch units or assemblies, which willretain their resistance characteristics even after such rigorous use as,for example, may be expected in the key switches of electronic organs.

Still another object is to provide a switch construction wherein thereis little or no tangential relative motion (wiping action) between thecontacts as they are opened or closed.

It is a further object of my invention to provide a leaf-type switchassembly in which the contact leaves are substantially self-adjusting.

A still further object is to provide an assembly of switch units whichmay be actuated by a single force not appreciably greater than theclosedcontact force required for a single unit.

These and other objects which will be apparent to those skilled in theart upon reading these specifications, I accomplish in thoseconstructions and arrangements of parts, of which I shall now set forthexemplary embodiments. Reference is made to the drawings forming a parthereof, and wherein:

Figure 1 is a perspective View of a preferred form of individual switchunit according to my invention.

Figure 2 shows a sectional view 22 of the unit of Figure 1.

Figure 3 is similar to Figure 2 except that the switch contacts areshown in a closed position.

Figures 4 and 5 are elevation views of other examples of circuit closingunits within the scope of my invention.

Figure 6 is a plan view of three adjacent assemblies of switch units ofthe type illustrated in Figure 1.

Figure '7 is a sectional view 7-! of the structure of Figure 6, showingan assembly actuated by a playing key and associated parts.

I shall describe my invention in exemplary embodiments having to do withkey switches for electrical musical instruments. Here the problems haveto do with the provision of structures which are simple, economical andnot liable to failure, as well as with the provision of structures whichare essentially self-adjusting and readily replaceable, as well as smallin size. My solutions of these problems lie in certain mechanicalconstructions hereinafter described.

Since for most key switches gradual contact means for the control oftransients or key clicks is highly desirable, my invention furtherincludes solutions of two interrelated problems. The first problem isthe provision of electric contact combinations which, when broughttogether under a continuously increasing force, will exhibit acontinuously variable contact resistance of wide range. My solution tothis problem lies in the use of combinations of contact materialshereinafter described which must, for reasons to be stated, be broughttogether without the tangential relative motion or wiping action usuallypresent, and in the use of combinations which are at the same timedesirable in electric circuit closing devices of the kind involved. Thesecond problem arising from my solution to the first is to provide meansfor closing the contacts without wiping action. My answer to the latterproblem is a switch unit or component which may be used either singly orin groups in a mechanical series, as will now be set forth.

One form of the basic unit or component of my switch invention isillustrated in Figure 1.

3 Here a spring leaf 2 is clamped adjacent one end between insulativesupports. Intermediate its ends there is attached to it an insulativemember 3, as by a rivet l or other means. The adjacent end of the springleaf 2 is bent upwardly and over, as indicated at 2a, so as to be spacedfrom the insulative member Contact elements I and E are locatedrespectively on end portions of the spring metal member 2a and theinsulative element 3. The contacts may take various forms as hereinafterset forth. The

member 3 may be of phenolic resin or other suitable insulative material,but may be electrically conductive if the contact is insulated from it.

The switch element illustrated in Figure 1 is one which can be operatedby a moving element engaging one of the switch parts and coacting withan opposed support to bring the contacts together. This operationinvolves moving the resilient element 2a toward the element 3; and itwill be seen that the contacts are brought together without anytangential motion or rubbing. Figures 2 and 3 on an enlarged scaleillustrate the contacts in open and closed position. The cantileverportion 2 of the spring will be flexed also in the operation of theswitch element to the extent required to bring one or the other of theelements 211 and 3 against the abutment referred to above.

Electrical contact from one of the circuit leads may be made directly tothe spring element 2, as at 212, beyond the engagement of the clampingelements 7. Because of the movement of the other end of the switchelement during operation, a flexible lead is required from the contact 5and is represented in Figure 1 as a flexible extension 5a of the contact5.

Modified structures of the basic element are illustrated in Figures 4and 5. In the first of these figures the cantilever spring element isstraight throughout its length. The insulative element 3 is fastened tothe spring element in the desired position by a rivet or the like -iaand is spaced therefrom by a collar 6.

In Figure 5 there is a straight spring element bearing the contact 5 anda second straight spring element to, paralleling the first and spacedfrom it. The spacing is maintained at the left hand ends of both springsby an intermediate insulative element la, the member 5a being free toslide between i and la, so as not to restrain the motion of the member 2when it is flexed. The two springs are connected intermediate their endsby an insulative coupling means 6a. In this instance the spring element311 bears the contact 5; and electrical connection to both springs maybe made at their left hand ends, as at 2b and 3b. This switchconstruction is mechanically satisfactory but is not as suitable as thestructures of Figures 1 and 4 for use in circuits where the open circuitelectrical capacitance between contact leaves must be kept at a minimum,e. g. in key switching circuits for electrical musical instrumentsenergized by potentials of high audio frequency.

The basic units of Figure 1 or the various modifications of Figures 4and 5 may be actuated singly or in multiples by any suitable means. Iprefer, in the case of a playing key switch, to employ the structureillustrated in Figures 6 and '7, the latter showing an assembly of foursimilar units whose respective parts are numbered so that theycorrespond to the nomenclature of Figure 1. Such a structure may beemployed for gradually and substantially simultaneously closing aplurality of circuits by a common actuator. Also, such an assembly maybe actuated by the relatively small force available with the usualplaying key construction. A nominal force for instance of live ouncesavailable at the inner end of a key under ordinary playing conditionswill operate a plurality of circuit closing units in a mechanical seriessuch as is illustrated in Figure 7 even though a force of as much asfour ounces may be necessary to bring the resistance of a single pair ofcontacts to a desired minimum value.

In Figures 6 and the insulative members 8 and 9 (corresponding to theclamping supports 1 of Figures 1, 4 and 5), provide support for thecantilever members 2, retaining lips ill struck from the cantileverspring members serving to prevent longitudinal movement of these membersin the exemplary construction. Electric connections to the members 2 maybe made at H. Thecontact members i and 5 are disposed in the same manneras in Figure l. The flexible extensions 5a of the contact members 5 maybe coated at their ends with a conductive paint and secured to aninsulative support 52 by resilient clips it to which may be solderedelectric connections as desired. A cross bar M, supported by studs l5and screws it, has an electrically insulative surface ll which acts as astop or abutment to the upward movement of the uppermost one of thecontact leaves 2a. Suitable proj ections it are disposed on the leaves2a to transmit from one unit to an adjacent unit a contact closing forceexerted by an actuator is, slidably mounted in the base member 2E9 andresting on a felt cushion 2i affixed to the upper surface of a keyspring 22. The spring 22 is held under an initial bending stress over afulcrum 2% on the playing key 23 by the heads of the screws 24 and 25,which are threaded into the inner end of the playing key. The key 23 issupported in the usual manner, as at El, and normally retained in theposition shown against a stop member 28 by a coil spring 2%.

The cantilever spring members 2 are flexible enough so that eachinsulative member 3 of each switch unit normally lies against theprojection l8 on the leaf immediately below. The lowermost insulativestrip 3 normally rests on the head of the actuator l9.

The operation of the playing key and switch assembly of Figure 7 may bedescribed by dividing the action into three phases in the followingorder. First, a depression of the right hand end of the key 23 exerts aforce through the spring 22 and actuator it upon the lowermostinsulative strip 3. As the lowermost unit 2 is deflected upwardly, theactuating force is transmitted through the offset portion 2a of thelowermost member 2 and its respective projection l3 to the insulativemember 3 next above in the switch. In a similar manner the actuatingforce is transmitted through the remaining insulative members S andtheir respective portions 2a and projections Hi. The uppermostprojection l8 will be restrained by the insulative surface ll of thecross bar abutment M, resulting in a simultaneous flexing of all offsetportions 2a of the cantilever members 2.

Were it not for the weight of the respective units and the small forcenecessary to deflect the cantilever members 2 from their normalpositions, all switch units if identical would begin to closesimultaneously. However, these last mentioned factors result in themeeting of the lower contacts slightly ahead of the meeting of the upperones. This difference in meeting is not of appreciable practicalsignificance, but if desired the offset portions 2a of the lower switchelements may be initially adjusted so that the contacts of allindividual switch units do meet simultaneously. During this first phaseof the key move ment, the key sprin 22 is partially deflected about thehead of the screw 24, which in a sense acts as a fulcrum during thefirst two phases, exerting an increasing force on the actuator is untilall contact surfaces l and 5 meet. In the second phase, as the key 23 isfurther depressed, the key spring 22 is additionally deflected about thehead of the screw 24 until a sufiicient force is exerted on the actuatoris to approximate the full desired closed contact force on all contacts.In the third phase, a further depression of the playing key merelydeflects the sprin 32 away from the head of the screw 24 withoutexerting any appreciable additional force upon the actuator l9 and allcontacts l and 5. This overtravel feature improves the touch of themechanism and prevents excessive forces from bein exerted on thecontacts after a desired minimum value of contact resistance has beenreached. The initial stress on the spring 22 can be changed by adjustingthe screw 25, thus providing means for varyin the approximate maximumforce which can be exerted on the series of switch units by the spring22 through the actuator It. The initial position of the left end of thespring 22 may be changed by adjusting the screw 24, thus providing meansfor determining the location of the actuator it with respect to theseries of switch units.

It can readily be seen that the structure of Figure 7 satisfies theobject of the invention relating to self-adjustment of the contactleaves, the offset portions 2a having sufficient stiffness to keep itscontact member I apart from its respective contact member 5. It can alsobe seen that since the structure comprises four springs in series theforce necessary to close all the con tacts is greater than the forcenecessary to close one set of contacts by only the sum of relativelysmall forces required to deflect the cantilever members 2 to theirrespective closed-contact positions plus whatever small forces arepresent due to the weight of the respective units.

In the broad aspects of my invention the structure thus far described isof general utility irrespective of the nature of th contact elements.For example, contact I may be a metallic contact of desired composition,a similar cooperating contact may be aflixed in the proper position onthe member 3, and the flexible conductor 5a may be of any kind desired.However, one of the objects of the invention in a narrower aspect is theprovision of resistive or gradual-acting switches for purpose set forthabove. In this event, the contact l may still be a metallic or otherrigid contact member, while the contact 5 be of resilient deformableresistive substance so that the efiect of varying pressure be tween thecontacts will be a variation of resistance in a circuit connected withthem. This variation of resistance may be brought about in various ways,one effective way being the shaping of the contact elements in such away that variations of contact pressure between them will producevariations in the area of their mutual contact. Thus the member 5 may beof resilient resistive substance and the flexible conductor 5a may be astrip-like prolongation of the same Substance.

I prefer to employ the extended portion 5a of the contact 5, which isdisposed between the free end of the insulative member 3 and a clip l3as a series resistor for the purpose known in art as anti-robbingthatis, the prevention of the interaction of one branch upon another-thusinsuring adequate flow of current through each switch when several ofthe circuits are operated in parallel. If the resistance of the flexibleconductor 5a is greater than that required in the circuit in which it isused, I may lengthen the previously mentioned coating of conductivepaint over an area such as at 3B in Figure 6 to decrease the seriesresistance. If the resistance is less than that desired, I may notch thestrip at one or more points 35 to increase the series resistance. I mayalso as a matter of design obtain a desired series resistance byemploying a contact 5 of material having characteristics mostsatisfactory for contact purposes, inserting between the contact 5 andthe insulative member 3 a strip of flexible material an extension ofwhich is suitable for supplying an approximate desired series resistancein the circuit. The above mentioned notching and coating adjustments maythen be used for desired final adjustments of series resistance.

It is not new to effect a variation of electrical resistance by varyingthe length cross-section of the current path through an elasticallyyielding resistor by the application of pressure to a metallic electrodein contact with the resistor, and various structures for this purposeare shown in U. S. Patent 1,448,681. In such prior structures thematerials were not subjected to a relatively large number of cycles ofresistance variation. In resistive playing key switches, subject torapid and repeated operation, my experience indicates that afterprolonged use the resistivity of such deformable materials increases atthe area subjected to deformation. Such increases in resisitivity alt-orthe lower limit of resistance to such an extent that the hitherto knowncoinbinations are unsatisfactory unless improved as discussedhereinafter. Since I have not as yet been able to produce an elasticallydeformable conductive material whose resisitvity does not increase asdescribed above after prolonged use, I have devised a combination ofmaterials with which such changes in resisitivity are not of seriousconsequence.

According to this phase of my invention, I eniploy as the contact l ofFigure l, for example, a rigid material of relatively high electrical resistivity, such as the material used in commonly known fixed carbonresistors employed in radio circuits. The contact member 5 of Figure 1may be a portion of a thin strip of relatively low electricalresistivity, elastically deformable mixture of a finely dividedconducting material, for example, carbon, in a rubber-like mater l, suchas neoprene, the mixture being processed in suitable manner to obtaindesired mechanical characteristics. The deformable material acts as asort of low resistance brush or flexible con tact which, upon theapplication of pressure, assumes the configuration of the highresistivity material, increasing the area of mutual contact. The totalcontact resistance is the sum of two series resistances which dependupon the resistivity of the respective contact materials; hence, if thegreater or" the two resistances is supplied by a contact material whoseresistance does not changein this case the rigid, relatively highresistivity material-a change in resistivity of th deformable material,which supplies in this case the lesser or" the two resistances, has lessefiect upon the total resistance than in the case or" a combination suchas employed by prior art workers. lhe greater the difference inresistivity between the materials of such a combination, the less willbe the effect of progressive changes in the resistivity of thedeformable material at the contact surfaces. I have found that aresistivity of the order of 30 ohm-centrimeters for the rigid materialand of the order of l ohm-centimeter for the deformable material areparticularly useful in electric musical instruments for connectingsources of electric oscillations to output and sound producing devices.A circuit showing such connections is illustrated and described inPatent No. 2,215,214 to Koch et al. An example of a desirable range ofresistance to be provided by a key switch is one having a higher limitof not less than 200,000 ohms and a lower limit of not more than 1,000ohms in key circuits employing antirobbing resistances of the order of5,000 ohms i series with each switch.

I may also reverse to physical form the materials I have just described.The contact I may be a molded button of an elastically deformablematerial of relatively low resistivity while the contact may be a rigidmaterial of relatively high resistivity. The contact 5 may either be astrip of material fixed to the insulative strip or it may be a resistivecoating thereon, provided with a suitable flexible conductor.

Although i have shown as an exemplary embodiment an electric musicalinstrument playing key switch, I do not wish to limit my invention tosuch switches. I may employ similar switches with or withoutmodification in conjunction with stop tabs to select tone color circuitsof the electric filter type, for instance, used in instruments whereincomplex electric oscillations are modified to obtain various tonecolors. I may also connect a mechanical series of switch units asdescribed herein in an electrical series to obtain a wide variation oiresistance, or I may use such units to remove gradually irom or replaceinto an electric circuit fixed resistances of desired values. Theusefulness of such switch units and assemblies described herein is notnecessarily limited to electric musical instruments. Such switches ormodifications may be found useful in other types of circuits whereinrelatively low values of electric current are to be controlled.

Modifications may be made in my invention without departing from thespirit of it. Having thus described m invention in certain exemplaryembodiments, what I claim as new and desire to secure by Letters Patentis:

1. Electric circuit switching means comprising in combination tworesiliently hinged, spaced leaves at least one of which is electricallyconductive, two coactive electric contacts respectively disposed on saidleaves, and a flexible, cantilever member having a iree end and a fixedend, said leaves being supported by the free end of said cantilevermeans.

, 2. The combination claimed in claim 1 wherein one or said leaves is anextension of said cantilever member which is electrically conductive andthe other of said leaves comprises a strip of electrically insulativematerial fastened to said cantilever member.

3. The structure claimed in claim 2 including flexible electricallyconductive means connected to the contact means disposed on saidinsulative leaf.

4. The combination claimed in claim 3 in which one of said contactscomprises a rigid material of relatively high electrical resistivity andthe other of said contacts comprises a material of relatively lowelectrical resistivity material which is elastically deformable uponcontact with said rigid contact.

5. The combination claimed in claim 3 in which one of said contactscomprises a material of rigid relatively low electrical resistivity andthe other of said contacts comprises a material of relatively highelectrical resistivity which material is elastically deformable uponcontact with rigid contact.

6. A resistive switch comprising the combination as claimed in claim 3including actuating means operative upon said leaves to bring saidcoactive contacts into a contacting relationship one with the other.

7. A resistive switch for gradually and substantially simultaneouslyclosing a plurality of electric circuits, said switch comprising incombination a plurality of flexible contact leaves rigidly andsubstantially parallelly mounted near one end, a first ser'es ofelectric contacts disposed respectively near the other end of saidleaves, a series of insulative strips affixed respectively to saidleaves intermediate their ends, the portion of each of said leavescontaining one of said first series of contacts being oiiset withrespect to its respective insulative strips, a second series of electriccontacts disposed respectively on said insulative strips and coactiverespectively with contacts of said first series, projections on each ofsaid leaves on the side opposite the respective contacts of said firstseries and bearing against the insulative strip amxed to an adjacentleaf in said plurality, stop means adjacent the outermost outward-facingprojection, an actuating member adjacent the outermost of saidinsulative strips operative to bring respective coactive contacts intocontactirn relationship with each other, and flexible electricallyconductive means connected to res ective contacts in said second series.

8. The combination claimed in claim '7, wherein the contacts in one oisaid serie of electric contacts comprise rigid material of relativelhigh electrical resistivity and the contacts in the other of said seriesof electric contacts comprise relatively low electri al resistivitymaterial which is elastically deformable upon contact with said rigidcontacts.

9. The combination as claimed in claim '7, wherein the contacts in oneof said series of electric contacts comprise rigid relatively lowresistivity material and the contacts in the other of said series ofelectric contacts comprise relatively high electrical resistivitymaterial which is elastically deformable upon contact with said contactsof rigid material.

10. The structure of claim '7 including a base upon which said pluralityof means is mounted, said stop means being mounted on said base, andsaid actuating member being a plunger slidable in said base.

11. In combination in a switch construction a first electric contactcomprising a rigid material of relatively high electrical resistivity, asecond electric contact coactive therewith and comprising a material ofrelatively low electrical resistivity which material is elasticallydeformable upon contact with said rigid material, and operating meansfor bringing said first means into contact with said second means.

12. In combination in a switch construction a first electric contactcomprising a rigid material having an electrical resistivity of theorder of 30 ohm-centimeters, a second electric contact comprising amaterial having an electrical resistivity of the order of 1ohm-centimeter and which is elastically deformable upon contact withsaid rigid material, and operating means for bringing said first contactunder pressure against said second contact.

13. In combination in a switch construction, a pair of contacts andmeans for bringing said contacts together under pressure, one of saidcontacts being a rigid member of relatively high resistivity, and theother of said contacts being a flexible, deformable member of relativelylower resistance, said last mentioned contact having an integralprolongation in strip form serving as a flexible, resistive lead.

14. In combination in an electric switching device, a stacked pluralityof resilient metallic leaves each rigidly and substantially parallellysupported near one end by insulative means, electric contacts disposedone to each of said leaves, a plurality of electrically insulativestrips aflixed one to each of said leaves, the portion of each of saidleaves containing said contacts being offset with respect to itsrespective insulative strip, electrical contacts disposed one to each ofsaid insulative strips on the sides thereof facing the respective leavesto which said strips are afiixed, said leaves having a projection on theface opposite said first-mentioned contact surfaces and bearing againstthe insulative strip affixed to an adjacent leaf in said series, stopmeans adjacent the outermost of said projections, and an actuatingmember adjacent the innermost of said insulative strips, whereby saidoffset portions may be flexed in bringing each of said first-mentionedplurality into contact with the corresponding surface of one of saidsecondmentioned plurality.

15. In a. switch construction a metallic spring member mounted as acantilever adjacent one end and bearing a contact adjacent its otherend, a leaf connected with said member intermediate its ends and bearinga contact opposite said first mentioned contact and normally spacedtherefrom, and a flexible electrical conductor extending from saidsecond mentioned contact.

16. The structure claimed in claim 15 wherein said second mentionedcontact and said flexible conductor are integral and are formed ofdeformable resistive substance.

17. In combination with the structure claimed in claim 10, a playing keyhaving a rearwardly extending portion, a resilient fiexible lever lyingalong said portion and having a rear end underlying said plunger, afulcrum for said lever intermediate its ends and mounted on said keyportion, and a pair of headed, threaded retaining members engaged insaid key portion, one of said members engaging the forward end of saidlever at one side of said fulcrum, and the other engaging said lever atthe other side of said fulcrum and at a point forward of the rear end ofsaid lever.

18. A variable resistance key action for a musical instrument,comprising the combination of at least one circuit closing componenthaving a fixed end and a free end, a pair of resiliently hinged, spacedleaves supported by the free end of said component, two coactiveelectric contacts respectively disposed on said leaves, a verticallydisposed actuating plunger operative to impart vertical motion to saidfree end, the electrical resistance of said component being dependentupon the force exerted by said plunger on said component, stop meansadjacent the free end of the outermost circuit closing component, aplaying key having a rearwardly extending portion, a resilient flexiblelever lying along said portion and having a rear end disposed againstsaid plunger, a. fulcrum for said lever intermediate it sends andmounted on said key portion, and a pair of headed, threaded retainingmembers engaged in said key portion, one of said members engaging theforward end of said lever at one side of said fulcrum, and the otherengaging said lever at the other side of said fulcrum and at a pointforward of the rear end of said lever.

19. In combination in a switch construction, a pair of contacts andmeans for bringing said contacts together under pressure, one of saidcontacts comprising a rigid material of relatively low electricalresistivity, and the other of said contacts comprising a material ofrelatively high electrical resistivity which material is elasticallydeformable upon contact with said rigid material.

RAYMOND P. MORK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,099,093 Kent June 2, 19141,143,487 Belin June 15, 1915 1,448,681 Stoekle Mar. 13, 1923 1,577,981Otto Mar. 23, 1926 1,658,666 Burgener Feb. 7, 1928 1,661,348 GrundrnanMar. 6. 1928 2,031,748 Victor Feb. 25, 1936 2,066,490 Sheatsley Jan. 5,1937 2,069,171 Merkle Jan. 26, 1937 2,215,124 Kock et al. Sept. 17, 19402,254,366 Hammond Sept. 2, 1941 2,266,856 Farny Dec. 23, 1941 2,480,945Marmont Sept. 6, 1949

